This invention relates generally to spindle extensions for milling machines and more particularly to a spindle extension having a supported arbor.
Milling machines are well known devices used for a wide variety of machining operations. A typical milling machine includes a mill head provided with a spindle that rotates with respect to the mill head. A cutting tool is attached to the spindle to perform work on a workpiece. A common prior art approach for fitting the tool to the spindle includes inserting a tapered shank of the tool into a tapered hole formed in the spindle. A retention knob provided on the shank is grasped by the milling machine's conventional draw bar assembly, which pulls the shank into the spindle to firmly attach the tool to the spindle. One problem with this arrangement is that standard cutting tools are too short to accommodate deep cavities required in some workpieces. While spindle extensions are available, these typically provide relatively limited extensions in the reach of the milling machine.
One known spindle extension comprises an arbor provided on one end with a tapered shank sized to fit the tapered hole of a standard milling machine spindle. The tapered shank is received in the tapered hole in order to connect the arbor for rotation with the spindle in the same manner that a cutting tool is conventionally connected to the spindle. The cutting tool is then attached to the end of the arbor opposite the spindle and is thus displaced from the spindle a distance equal to the length of the arbor. However, with this type of spindle extension, the arbor is not supported in any way other than by the tapered shank spindle connection. This results in a cantilevered arrangement that is susceptible to excessive flexure. Accordingly, such conventional spindle extensions are limited to arbor lengths of about six inches, and such extensions do not function well in high speed, heavy cutting machining operations. At greater lengths, the arbor and/or the tool tend to experience instability that can result in lack of dimensional control, poor surface finish and tool failure.
Accordingly, there is a need for a milling machine spindle extension that provides considerably greater tool reach in high speed milling machines in a stable manner.